粒子跟踪的时候位置信息为什么和四面体网格有关？

Each particle position is defined by topology (i.e. which decomposed tet cell it is in) and geometry (i.e. where it is in the cell).

In previous versions of OpenFOAM, the particle tracking algorithm moved particles successfully and efficiently in meshes of unstructured, arbitrarily polyhedral cells, in parallel, even in cases where faces of cells were significantly non-flat. Its primary limitation was that it was only applicable where all cells were strictly convex and, in the worst case, concave cells caused a solver to hang indefinitely. Such cells often exist in meshes generated by automatic tools, such as snappyHexMesh, especially at all refinement interfaces where it naturally produces cells that are not strictly convex. To overcome this limitation, the tracking algorithm has been re-written to track particles on an implicit decomposition of each cell into tetrahera as shown.